When we hear vitamin D, most of us think of sunshine, supplements, or fortified milk. But here’s something that might surprise you—vitamin D isn’t technically a vitamin at all. It’s actually a hormone.
What Makes Vitamin D a Hormone?
Unlike typical vitamins that must be obtained entirely through diet, vitamin D is produced by the body itself—specifically in the skin when exposed to sunlight.
Once it’s made (or consumed through food and supplements), vitamin D undergoes two important transformations: first in the liver, and then in the kidneys, where it becomes its active form known as calcitriol (1,25-dihydroxyvitamin D).
Calcitriol acts as a hormone, traveling through the bloodstream to regulate vital body functions—especially the absorption and balance of calcium and phosphorus, minerals essential for strong bones and overall health.
Why Vitamin D Is Vital
Vitamin D’s hormone-like actions are crucial for:
- Enhancing calcium and phosphorus absorption in the gut
- Reducing calcium loss through the kidneys
- Supporting bone growth and remodeling in both children and adults
Without enough active vitamin D, your body struggles to absorb calcium efficiently. Over time, this can lead to weak bones, fractures, or conditions like osteoporosis and rickets.
A Hormone With a Broader Role
Beyond bone health, research continues to uncover vitamin D’s influence on other aspects of wellness. Studies suggest that adequate vitamin D levels may help:
- Support heart health
- Lower the risk of certain cancers
- Improve immune function
- Reduce the risk of respiratory infections
While these findings are promising, scientists are still exploring the full extent of vitamin D’s role in preventing chronic diseases.
Why We Still Call It a “Vitamin”
Despite functioning like a hormone, vitamin D remains grouped with vitamins largely for historical reasons. The word vitamin comes from vita, meaning life—a fitting description, since vitamin D is indeed essential for life and long-term health.
The Bottom Line
Vitamin D behaves far more like a hormone than a typical nutrient, helping regulate calcium balance, bone strength, and possibly even immune and cardiovascular health.
While some can be obtained from food, sunlight remains the most natural source—triggering your body’s own production of this powerful hormone.
Because everyone’s needs are different, it’s important to test your vitamin D3 levels to determine the right dosage for you.
If you’re unsure about your levels or whether you need supplementation, talk to Dr. Tan for personalized guidance on optimizing your vitamin D for better bone and overall wellness.